Expandable stent apparatus and method

ABSTRACT

An expandable stent has a sheeted material which is expanded from a compacted configuration to an expanded configuration. The sheet is maintained in the compacted configuration at least in part by operation of a dynamic force, and the expansion occurs at least in part by removal of the dynamic force. In preferred embodiments, a biocompatible sheeted material is wrapped around a split reed grasper to produce a compacted configuration, and the split reed grasper is rotated to maintain the compacted configuration during insertion of the stent into a patient. The rotation is continued while the stent is positioned, and then the rotation is stopped or slowed to permit expansion of the sheet.

RELATED PATENTS

This application is a continuation of U.S. patent application Ser. No.09/780,883 filed Feb. 9, 2001, now U.S. Pat. No. 6,406,487, which is acontinuation of U.S. patent application Ser. No. 09/372,711, filed Aug,11, 1999, now U.S. Pat. No. 6,187,015, which is a continuation of U.S.patent application Ser. No. 08/850,320 filed May 2, 1997, now U.S. Pat.No. 5,957,929.

FIELD OF THE INVENTION

This invention relates to expandable stents.

BACKGROUND OF THE INVENTION

Stents are endoprostheses which can be deployed into the lumen of anartery or vein, a common bile duct, the urethra or other bodypassageway. Stents may be employed in such passageways for manypurposes, including expansion of a lumen, maintenance of the lumen afterexpansion, and repair of a damaged intima or wall surrounding a lumen.With respect to arteries, for example, stents may be used as, or inconjunction with, intralumenal grafts in the maintenance of patency of alumen following angioplasty. In such cases a stent may be used toprevent restenosis of the dilated vessel, to prevent elastic recoil ofthe vessel, or to eliminate the danger of occlusion caused by “flaps”resulting from intimal tears associated with the angioplasty. In otherinstances, stents may be used to treat aneurysm, tears, dissections andother continuity faults, as, for example, in the splenic, carotid, iliacand popliteal vessels. By way of further example, it is known to use astent to maintain the patency of a urethra compressed by an enlargedprostate gland.

In one class of expandable stents commonly referred to as “rolled”stents, a sheeted material is rolled onto the outer distal circumferenceof a support member or “core”. The sheeted material is then positionedat a targeted treatment area and expanded. Rolled stents can becharacterized according to: (1) the method by which the rolled sheet ismaintained in a compressed configuration; and (2) the method by whichthe sheet is expanded.

Lane, Self Expanding Vascular Endoprosthesis for Aneurysms, U.S. Pat.No. 5,405,379 (Apr. 11, 1995) describes a stent which employs a selfexpanding sheet. The sheet is forcibly rolled into a compressedconfiguration, and then inserted into a catheter to maintain thecompressed configuration. Expansion takes place by ejecting the sheetfrom the end of the catheter.

Kreamer, Intraluminal Graft, U.S. Pat. No. 4,740,207 (Apr. 26, 1988)describes a rolled stent in which a sheet of stainless steel is rolledaround an angioplasty type balloon. After being introduced into atreatment area, the sheet is expanded by inflating the balloon with afluid. In this case compression is maintained during the early stages ofdeployment by the relaxed nature of the sheet in the compressedconfiguration, i.e., the internal mechanical resistance of the sheet todeformation. Expansion of the sheet, on the other hand, occurs underradial pressure exerted by the expanding balloon.

Sigwart, Intravascular Stent, U.S. Pat. No. 5,443,500 (Aug. 22, 1995)describes a stent in which a flat sheet is perforated to form areticulated or lattice type structure having a ratcheting lockingmechanism. Compression in stents according to the Sigwart patent aremaintained by a holding wire or adhesive, and the sheet is contemplatedto be expanded under the influence of an angioplasty balloon.

Sigwart also describes another stent comprising an elastic stainlesssteel mesh. The diameter of the mesh is slightly larger than the normalinner diameter of the vessel to be treated, so that the mesh can exert aresidual radial pressure on the arterial wall after being implanted.Before being introduced into a patient's blood vessel the stent isreduced in diameter. The reduced diameter is maintained while advancingthe stent into a target treatment area by an outer sleeve. Once thedevice is implanted, the stent is deployed by withdrawal of the outersleeve. In this instance, compression is thus maintained by the outersleeve, and expansion is achieved by removal of the outer sleeve.

Alfidi and Cross, Vessel Implantable Appliance and Method of ImplantingIt, U.S. Pat. No. 3,868,956 (Mar. 4, 1975) describes a stent whichutilizes a recovery alloy such as nitinol. In such stents an initialexpanded configuration is permanently set into the alloy by heating thematerial to a relatively high temperature while the alloy is maintainedin the expanded configuration. The alloy is then cooled and deformed toa compressed configuration. The compressed configuration is retained atroom temperature, but recovers to the expanded configuration whenreheated to a transition temperature. Here, compression is maintainedduring the early stages of deployment by the internal mechanicalresistance of the alloy against deformation, and the sheet is expandedunder the influence of heat.

These and all other known teachings reflect the accepted wisdom thatrolled stents are to be maintained in their compressed configurations bythe operation of static forces (e.g., biasing produced by the internalmechanical resistance of the sheet to deformation, presence of holdingwires, outer sleeves and so forth), while expansion of the sheetedmaterials is to be produced by application of a dynamic force (e.g.,radial pressure exerted by an expanding balloon, application of heat,removal of a holding wire or sheath, and so forth). While suchstrategies undoubtedly have their benefits, it is useful to have stentswhich operate outside of these accepted constraints.

Where the stent is to be deployed in very small vessels of the body,such as the arteries in the brain, the size of the stents is quitesmall, and the material used for the stents is on the order of0.0001–0.0004 inches thick. The small size and extreme thinness of thestent material makes it difficult to deploy the stent using the typicalpush-pull type deployment mechanisms generally used for stents. Thefrictional force exerted on the stent by the catheter sheaths and coresas they slide over the stent often tears the stent. In our co-pendingU.S. patent application Ser. No. 08/762,110, filed Dec. 9, 1996, weprovide a number of devices that do not require any sliding movement ofthe stent or catheter sheath relative to each other. The devicesdescribed below provide additional mechanisms and methods for deployingstents while minimizing the frictional forces operating between thestents and the catheters used for their insertion.

SUMMARY OF THE INVENTION

Stents for intra-cranial use and methods for using these stents aredescribed in detail below. The physical characteristics of prior artballoon expandable stents and self expanding stents make them clearlyunsuitable for intra-cranial use, because of their delivery profile,their lack of flexibility and their tendency to temporarily occlude thevessel during deployment. They have not been proposed for intra-cranialuse. Palmaz stents, Palmaz-Schatz™ stents, Wallstents, Cragg stents,Strecker stents and Gianturco stents and other stents are too rigid toallow placement in the cerebral blood vessels, some require a balloonfor deployment, and all are too open to occlude or prevent blood flowinto an aneurysm. Presented below are several embodiments of stentssuitable for intra-cranial use, along with methods for using thesestents to treat intra-cranial vascular disease.

The self expanding rolled sheet stent is suitable for use in theintra-cranial arteries. The rolled sheet is made of Elgiloy™, nitinol,stainless steel, plastic or other suitable material, and is impartedwith resilience to urge outward expansion of the roll to bring therolled stent into contact with the inner wall of a diseased artery. Therolled sheet is adapted for easy insertion and non-deforming radialflexibility to facilitate tracking along the tortuous insertion pathwaysinto the brain. In some embodiments, as much of the material of thestent is removed as is consistent with eventual creation of a solidwalled stent upon unrolling of the stent within the blood vessel. Theunrolled stent may be two or more layers of Elgiloy™, thus providingradial strength for the stent and creating at least a slight compliancemismatch between the stent and the blood vessel, thereby creating a sealbetween the stent and the blood vessel wall. For placement, the stent istightly rolled upon or captured within the distal tip of an insertioncatheter. The release mechanism is extremely low profile (3 Fr or less),and permits holding the rolled stent in a tight roll during insertionand permits atraumatic release when in the proximity of the site ofarterial disease, without completely occluding the vessel with thedeployment catheter. The stent can be placed in the intra-cranial bloodvessels (arteries and veins) of a patient to accomplish immediate andcomplete isolation of an aneurysm and side branches from the circulatorysystem. The stent can be placed so as to partially occlude or modifyblood flow into an aneurysm. The stent can be placed so as to allow forinjection of coils (GDC coils or Gianturco coils) or embolic materialinto an aneurysm and prevent wash-out of the coils or embolic material.The stent may be placed across a target site such as an aneurysm neck,origin of a fistula, or branch blood vessels feeding a tumor in order toredirect the flow of blood away from the target. It can be used as astand alone device which is left in the intra-cranial arterypermanently, or it may be used as a temporary device which allows forimmediate stabilization of a patient undergoing rupture of a bloodvessel an aneurysm or awaiting open skull surgery for clipping orresection of an aneurysm. The stent can be used for stabilization andisolation of a vascular defect during surgery of the vascular defect.Another advantage of this type of stent is that it can be wound downshould repositioning be required prior to full release. It is possibleto rewind and reposition or remove the device using a crooked rotatingwire or other grasping tools.

The present invention is directed to expandable stents having a sheetedmaterial configurable in both a compacted configuration and an expandedconfiguration, in which the compacted configuration during deployment ismaintained at least in part by operation of a dynamic force, andexpansion to the expanded configuration occurs at least in part byremoval of the dynamic force.

In preferred embodiments, a biocompatible sheeted material is wrappedaround a retaining wire to produce the compacted configuration, and theretaining wire is rotated to maintain the compacted configuration duringinsertion of the stent into a patient. The rotation is continued whilethe stent positioned, and then the rotation is stopped or slowed topermit expansion of the sheet. Counter rotation may be used to enhanceexpansion, if desired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the vasculature of the brain showing atypical placement of an intra-cranial stent.

FIG. 2 is schematic diagram of the vascular of the brain illustratingthe circle of Willis and arteries supplying the circle of Willis.

FIG. 3 is a diagrammatic representation of a stent according to thepresent invention.

FIG. 4 is a diagrammatic representation of a motor drive used for thestent and its connection to the system.

FIGS. 5 a, 5 b and 5 c are a diagrammatic representations of a the stentin the process of deployment.

FIGS. 6A, 6B, 6C, 6D and 6E illustrate various methods of attaching anddetaching a stent from the insertion catheter.

FIG. 7 shows an embodiment of the rotating stent deployment system witha tear-away tab release.

DETAILED DESCRIPTION OF THE INVENTIONS

The stent delivery system is particularly well suited for delivery ofstents into very small vessels in the body, such as the blood vesselswithin the brain. FIGS. 1 and 2 show the vasculature of the brain insufficient detail to understand the invention. The brain 3 is suppliedwith blood through the carotid and the vertebral arteries on each sideof the neck. The important arteries include the common carotid artery 4in the neck, which will be the most common access pathway for the stent,the internal carotid 5 which supplies the opthalmic artery 6. Theexternal carotid 7 supplies the maxillary artery 8, the middle meningealartery 9, and the superficial temporal arteries 10 (frontal) and 11(parietal). The vertebral artery 12 supplies the basilar artery 13 andthe cerebral arteries including the posterior cerebral artery 14 and thecircle of Willis indicated generally at 15. Also supplied by theinternal carotid artery are the anterior cerebral artery 16 and themiddle cerebral artery 17, as well as the circle of Willis, includingthe posterior communicating artery 18 and the anterior communicatingartery 19. These arteries typically have an internal diameter of about 1mm to 5 mm, most commonly from 2–4 mm. The methods and devices describedherein allow access to these arteries and placement of a stent in thesearteries. In FIG. 1, the insertion catheter 2 and stent 1 are shown inan exemplary use, threaded through the common carotid artery 4 and theinternal carotid artery 5, with the stent extending into the anteriorcerebral artery 16. The rotating wire 20 extends from the proximal endof the insertion catheter 2 to the distal end, and into the stent toimpart rotation to the stent.

FIG. 2 shows the same blood vessels in a schematic view that betterillustrates the circle of Willis and the arteries which supply thisimportant anatomic feature. The circle of Willis 15 is a ring ofarteries connecting the internal carotid arteries and the basilar artery(and hence the left and right vertebral arteries) to the anteriorcerebral arteries 16, middle cerebral arteries 17 and posterior cerebralarteries 14. The system provides a redundant supply of blood to thecerebral arteries. Aneurysms, fistulas, AVM's and tumors occurringinside the brain, in the intracranial portion of the carotid arteries,vertebral arteries and basilar artery, in the circle of Willis or evendeeper within the brain may be treated with the stents and deliverysystems described below. FIG. 2 shows an exemplary use in which adelivery catheter 2 is inserted through the aorta into the commoncarotid, internal carotid and through the circle of Willis 15 into themiddle cerebral artery 17 to treat an aneurysm 21 with a stent which isdeployed while being rotated by rotating wire 20, as explained below.

In FIG. 3, the structure of the stent and stent delivery system areshown in detail. The stent 10 used with the system generally comprises arolled sheet 22. The rolled sheet is sized appropriately to both fitwithin a delivery sheath when rolled tightly, and fit snugly within ablood vessel when released and allowed to open to a loosely rolledconfiguration. The sheet 22 is releasably coupled to the insertioncatheter 2 via the retaining wire 20 which has a tightly bent crook 23which grasps the inner edge 24 or the stent. The retaining wire 20 isrotated in the direction of arrow 25 such that the sheet 22 tends towrap around the retaining wire 20. Rotation in this manner tends tocause the sheet 22 to assume an at least partially compactedconfiguration. The sheet is 22 initially wrapped around the retainingwire and slipped into the distal end 26 of the insertion catheter. Oncecompacted in this manner, the stent 10 can be introduced into theinsertion catheter 2 for deployment into an artery or other passageway.When inserted into the insertion catheter 2, the retaining wire securelyholds the stent in the tight roll within the insertion catheter.

The proximal end of the stent delivery system is shown in FIG. 4. Theretaining wire 20 is attached at its proximal end 30 to a proximal hub31 and an electric motor 32 which is housed within the handle 33. Themotor 32 is used to rotate the retaining wire 20 and the stent 1. Themotor may be operated to rotate the retaining wire 20 and the stent 1 inthe direction which urges sheet to tighten upon itself and remain in asmall diameter configuration (indicated by arrow 25). The motor iscontrolled with a spring loaded thumb slide 34. A portion of the stent 1passes through a catheter 2, but during at least a portion of its travelduring deployment in a target lumen, the sheet is maintained in acompacted configuration at least partially as a result of continuedrotation of the stent 1 by the motor 32.

The motor 32 is presently contemplated to have an operational range ofbetween zero and 200 revolutions per minute (rpm). It is consideredadvantageous for the motor 32 to include a variable speed control, andthe motor may have a reverse mode. The motor may be battery operated toavoid the need for a power cord. It is also desirable to have a manualturning device, such as the proximal hub 31 which is connected directlyto the retaining wire 20, or to the motor 32, or indirectly coupled tothe retaining wire 20 through a clutch mechanism. For small rotationsneeded for some manipulations of the stent during and after placement,it is sufficient to rotate the entire handle and motor assembly by hand.A typical retaining wire comprises a wire 100–175 cm long, and maymeasure about 0.005 to 0.020 inches (5–20 mils, or 0.1–0.4 mm) indiameter. Of that length, about 0.5 cm at the distal end is bent aroundto form the retaining wire crook. The proximal end is attached to theproximal hub connector in motor and handle assembly. The retaining wiremay be releasably attached with connections such as the couplingstypically used for rotational atherectomy catheters and intravascularultrasound catheters. Preferred materials for the retaining wire includestainless steel and nitinol.

Turning in greater detail to specific elements of the stent 1, it shouldbe apparent that the sheet 22 can have any suitable composition, surfacecharacteristics, shape, thickness, elasticity and so forth. When used inthe illustrated use for blocking off side wall aneurysms or side vesselsin an artery, the stent sheet material is preferably made of Elgiloy ornitinol (with nickel-rich nitinol being preferred). The sheetspreferably comprise biocompatible material, but there may becircumstances in which stent is to be used for occlusion or tissuedisruption, in which case a non- or only minimally compatible materialmay be preferred. Biocompatible materials include various metals,synthetics and ceramics, and may also include living tissue or acomposite of living tissues and non-living material such as described inTuri, Composite Intraluminal Graft, U.S. Pat. No. 5,556,414 (Sep. 17,1996). Thus, the terms “sheet” and “sheeted material” are used herein ina very broad sense, including relatively thin meshes and other materialshaving a relatively large flattened surface.

Sheets according to the present invention may advantageously have asmooth outer surface to minimize trauma to tissues with which the sheetcomes in contact. The surface may also include an anti-restenosiscoating such as heparin, fibrin or a fibrin/elastic compound. Otheruseful coatings, such as a degradable mucin or other coating to minimizefriction, may also be used. The stent may be treated so as to beradioactive, in order to minimize hyperplasia and excessive neointimalgrowth. A radiographically opaque coatings, such as tin or platinum,have proven to enhance radiographic visibility of the stent during andafter deployment. Tantalum plating of about 1000 to 10,000 Å thicknessis sufficient to provide good visibility of the stent when rolled inmany layers within the insertion catheter, and a plating of 500 to 5000Å on both sides of the sheet is sufficient for good visibility of thestent when expanded into just a few layers within the blood vessel.

As with the other characteristics mentioned herein, there are numerouscontemplated variations for the shape and thickness of the sheet. Thesheet should have sufficient size and stiffness to handle the relativelyhigh stresses involved. Thus, the length of the sheet employed to treataneurysms of the carotid arteries in an adult male may advantageouslymeasure about 2.5 mm in longitudinal length 1 and about 40 mm in wraplength w. For aneurysms of the cavernous carotid arteries, the stent maybe telescoped to cover distances as much as 10 mm or more. Where thestent is deployed in smaller vessels, however, such as the cerebralarteries, the corresponding dimensions may be 1 mm in length and 20 mmin wrap length. The thickness may measure 0.0001″ to 0.0004″ (0.1–0.4mil, or 0.0025–0.01 mm) when the sheet is made of Elgiloy. The thicknessof 0.0002–0.0003″″ (0.2–0.3 mil, or 0.0050–0.0075 mm) has worked best inbench tests and animal studies, resulting in negligible crimping fromthe crook and providing for easy deployment without the tearingassociated with push-type deployment methods. Nitinol sheets may beslightly thicker and may allow for greater radial force applied by thestent against the blood vessel wall. The wrap length of the stent mayvary according to the size of the target vessel and the number ofoverlapping layers desired in the deployed configuration.

The stent sheets may be perforated to any degree necessary to encouragetissue ingrowth or to allow for some blood flow through the stent wall.Although the sheets illustrated are rectangular or ribbon shaped, thesheets used for the stents need not be rectangular. A triangular shape,for example, may also be feasible, with either an edge or a point of thetriangle being grasped by the retaining wire. The wrap length of thesheet may be variable, and may be long enough to wrap the sheet arounditself three, four, five or more times, or it may be short enough sothat the wrap length is substantially equal to the circumference of thetarget vessel, in which case the sheet will have a single layer afterdeployment. In such cases, it may be desirable to translate theretaining wire within the lumen back and forth during deployment toreduce the possibility of gaps. The stent may be telescoped to allow forgreater length than its straight rolled configuration would otherwiseallow. Also, the rotational method of deployment may be used with theextreme cases of a wire coil stent wherein the stent comprised a coil ofround or square wire (as opposed to the ribbon shape used in theillustrations).

The use of Elgiloy™ or nitinol provides elasticity that is suitable foreasy deployment of the stent, providing for adequate self expandabilityand also providing adequate strength for the stent after deployment. Thecrimping at the inner edge of the stent, where the crook grasps thesheet, is negligible or acceptably small with Elgiloy and nitinol. Othermaterials may be used which provide relatively more or less of a selfexpanding quality. One alternative is to make the sheet with materialthat has high elasticity, and will expand to a substantiallypredetermined shape upon cessation of rotation. In other instances, thesheet may have little or no elasticity, and may be optimally deployed byceasing rotation, and then unwinding the sheet by rotation in theopposite direction, by balloon expansion, or otherwise applying activeforce upon the sheet. There may also be greater elasticity in onedimension than in another

Lumenal deployment occurs by rotating the stent 1 while extending itfrom the open distal end of the catheter. While still under theinfluence of continued rotation, the stent 10 is pushed from the distalend of the insertion catheter, using the motor and handle assembly. Thestent is navigated through any length of blood vessel while rotating,and fed to a target area for deployment, where the rotation is stoppedor even reversed slightly to unwrap the sheet 22. Simple manual rotationof the retaining wire may be used to assist in proper deployment. Thestent 1 is then pushed, pulled, or otherwise manipulated to free theretaining wire 20 from the sheet, and the stent is withdrawn. FIGS. 5 a,5 b and 5 c illustrate the method of deployment of a stent which isenabled by the device. In FIG. 5 a the stent 1 is positioned at thedistal end of the insertion catheter 2. The stent is still wrappedaround the retaining wire and secured by the crook of the wire. In FIG.5 b, the retaining wire 20 is rotated in the direction necessary totighten the stent, and this rotation causes the stent to tighten into atighter roll (the diameter may remain the same or become smaller,depending on the speed of rotation and the flexibility of the stent) andalso causes the stent to rotate with the retaining wire. As illustratedin FIG. 5 b the stent 1 is advanced out insertion catheter 2. Thelongitudinal movement of the stent within the insertion catheter isfacilitated by the rotation, and the stent 1 is maintained in atightened configuration by rotation of the retaining wire 20 in thedirection of arrow 25. The stent also does not spread longitudinallyduring the rotation, and this also facilitates deployment (although therolled sheet may be telescoped to spread it out and cover a length ofthe blood vessel). Finally, as shown 5 c, the stent is pushedlongitudinally out of the distal end of the insertion catheter and intothe lumen of the blood vessel 35 in position to close off the aneurysm36. The retaining wire may be used to push or pull the stent into betterposition as it is rotating. Rotation is ceased when the position isacceptable, whereupon the stent opens fully. Fully unwinding of thestent can be ensured by counter-rotating the retaining wire (with themotor in reverse, or by hand turning the handle or the proximal hub). Torelease the stent, the retaining wire is pushed distally until the crookslips off the stent. The retaining wire may again be used to push orpull the stent into better position, or adjust the inner layer tocompact or spread the stent longitudinally. The crook may be used tore-engage the stent and resume rotation (in order to move or remove thestent) by advancing the retaining wire to a position distal of the stentand carefully slipping the crook between the layers and resumingrotation. With this technique, the stent may be used as a permanentstent or as a temporary stent, for blood vessels deep within the body,and in particular for blood vessels within the brain. When used as apermanent stent to occlude and aneurysm, the stent may constitute theprimary treatment for the aneurysm. When used as a temporary stent, thestent may be placed to occlude an aneurysm before invasive surgery suchas aneurysm clipping or ligation, thereby eliminating much of the riskinherent in open surgical techniques for treating aneurysms within thebrain. After a successful clipping or ligation, the stent can bere-engaged and rotated, and pulled into the distal end of the insertioncatheter. It should be apparent that, when used as a temporary stent inan interoperative setting, the retaining wire may be left in place andneed not be removed from the stent at any time. The stent may also beused to control blood flow through the neck of an aneurysm inconjunction with coils, embolic materials or other devices, or it mayoperate as a primary treatment.

Other embodiments of distal rotatable and releasable connection may beused. As discussed above, the rotation of the stent is accomplished withthe crooked retaining wire 20. Other stent rotation means are shown inFIGS. 6A through 6E. In FIG. 6A, the retaining means comprises arotating shaft 37 with a split reed grasper 38 disposed on the distalend of the rotating shaft. The inside edge of the stent is trapped inthe split reed, so that when the rotating shaft is spun from the distalend the stent is spun at the distal end. The stent is released when thesplit reed is pulled into the insertion catheter. FIG. 6B includes acompression ring 39 and pullwire 40 (which extends to the proximal endof the catheter) which can be used to compress the split reed duringinsertion and rotation, after which the compression ring can be pullproximally to allow the split reed to open slightly and release thestent. In FIG. 6C, the retaining means comprises a hollow shaft 41 (suchas a hollow guidewire) combined with a pullwire retainer 42 runsgenerally through the center of the hollow shaft and but exits thecenter of the shaft though proximal wire port 43 p, then runs over theinner edge of the stent before reentering the hollow shaft throughdistal wire port 43 d. The stent is thereby trapped by the pullwireretainer 42. Rotation of the hollow shaft 41 causes rotation of thestent to tighten the stent configuration during insertion andlongitudinal movement. When the stent is properly positioned, rotationis stopped and the pullwire retainer is pulled proximally to release thestent. FIG. 6D shows the crooked retaining wire 20, and the stent 1which is trapped in the crook 23. The inner edge 24 of the stent isfolded back, toward the outside surface, to form a flap 44. Thisoutwardly facing flap provides extra holding power for the crook duringrotation of the stent. FIG. 6E discloses yet another embodiment in whichthe stent 1 is retained between two spinning wires, a mounting spinningwire 45 and a retaining pullwire 46. Both wires extend to the proximalend of the insertion catheter 2 where they are attached to the proximalhub and motor. At the distal end, the mounting spinning wire is fixed tothe guidewire tip 47, and the retaining pullwire is not fixed andtherefore can be moved longitudinally in relation to the mountingspinning wire. The space between the wires is maintained tight by therings 48 d and 48 p which are fixed to the mounting spinning wire, andthrough which the retaining pullwire 46 may move longitudinally. Thestent will rotate with the wires, and release may be accomplished bypulling retaining pullwire 46 proximally away from the stent. The stentmay be crimped, folded or provided with a beaded edge 49 on the insideedge 24 to ensure a good grip on the stent. Each of the embodiments canincorporate an integral guidewire tip which extends distally from thecrooked retaining wire or the rotating hollow shaft, as the case may be.Alternatively, the device may be inserted in over the guidewire fashion,or in rapid exchange fashion (in which case the insertion catheter maybe provided with a monorail tip).

In FIG. 7 another embodiment of the rotating and retaining means isillustrated. The retaining means comprises a core 50 which includes aretaining wire 51 which is bonded at or near the inner edge 24 of thesheet 22. The starter notch 52 on the stent, located to correspond tothe diameter of the core 43, creates a tear line 53 which separates thesheet into the major portion of the sheet 22 which will remain in theblood vessel after deployment, and a small tear-away tab 54 which willbe torn from the major portion of the sheet in order to release thestent. During deployment the core 43 and the inner wire 44 are rotatedto tighten the stent and facilitate longitudinal movement of the stentout of the distal end of the catheter and within the lumen of the bloodvessel. When the stent is properly placed, the small tear-away tab canbe retracted proximally using several gentle tugs, which strips off themajor portion of the sheet 22 from the inner wire 44. The bonding can beachieved using cyanoacrylate adhesive (super glue) or any other suitableadhesive.

The various embodiments of the releasable retaining mechanism provide adynamic rotational force that maintains the stent in a configuration inwhich longitudinal movement is facilitated. Rotation may be at suchspeed as to spin the stent into a smaller diameter, but this is notstrictly necessary. It is sufficient that the stent be urged toward amore tightly wound condition, such that the outer layers may slide morefreely over each other and past the inner surfaces of the catheter andblood vessel. The process is similar to that used to remove a roll ofpaper from a mailing tube, which often requires that the roll be twistedfrom an inside layer to loosen the roll within the mailing tube whilethe roll is pulled from the mailing tube. In this analogous situation,it is apparent that the roll of paper need not be spun so much that isactually takes on a smaller diameter, and that it is sufficient toremove the outwardly compressive force exerted by the inner rolls asthey resiliently try to expand against the outer layers. We say that theroll of paper is rotated to urge the roll toward a smaller diameterconfiguration, realizing that the smaller diameter configuration neednever be achieved. We also refer to the configuration achieved byrotation as the compacted configuration, realizing that this includesconfigurations in which inner layers are rotated into a tighter roll butouter layers may be tightened into a smaller diameter or may merelybecome loose compared to the inner layers, depending on the rotationalspeed applied. Such a compacted configuration is maintained at least inpart by operation of the dynamic force applied by rotation, andexpansion to the expanded configuration occurs at least in part byremoval of the dynamic force.

Thus, while specific embodiments and applications of expandable stentshave been disclosed and described in reference to the environment inwhich they were developed, they are merely illustrative of theprinciples of the inventions. Although described in reference to thetreatment of blood vessels, the devices may be employed in any vessel ofthe body. It should be apparent to those skilled in the art that manymore modifications besides those already described are possible withoutdeparting from the inventive concepts herein. For example, it iscontemplated that new and better materials be discovered for use andintravascular stents. Similarly, it is possible to devise a number ofreleasable attachment means in addition to those illustrated. Theinventive subject matter, therefore, is not to be restricted except inthe spirit of the appended claims.

1. A stent and stent delivery system for inserting a stent into a bloodvessel and deploying the stent at a target site within the blood vessel,said stent delivery system comprising: an insertion catheter ofappropriate diameter, length and flexibility for insertion into theblood vessel and navigation within the blood vessel to a location at ornear the target site; a stent comprising a rolled sheet stent having asmall diameter rolled configuration in which the stent fits within thelumen of the insertion catheter and a large diameter rolledconfiguration in which the stent fits within the blood vessel; a splitreed grasper secured to the rolled sheet stent and extending to theproximal end of the insertion catheter; and a means for rotating thesplit reed grasper, thereby causing rotation of the rolled sheet stentand facilitating longitudinal movement of the stent; wherein the meansfor the rotating split reed grasper comprises a hand held motor.
 2. Thestent delivery system of claim 1 wherein the split reed grasper isreleasably connected to the rolled sheet stent.
 3. The stent deliverysystem of claim 1 wherein the stent comprises a sheet of nitinol.
 4. Thestent delivery system of claim 1 wherein the stent comprises a sheet ofperforated material.
 5. A stent and stent delivery system for insertinga stent into a vessel of the body and deploying the stent at a targetsite within the vessel, said stent delivery system comprising: aninsertion catheter of appropriate diameter, length and flexibility forinsertion into the vessel and navigation within the vessel to a locationat or near the target site; a stent having a small diameterconfiguration in which the stent fits within the lumen of the insertioncatheter and a large diameter rolled configuration in which the stentfits within the vessel; a split reed grasper secured to the stent andextending to the proximal end of the insertion catheter; and a means forrotating the split reed grasper, thereby causing rotation of the stentand facilitating longitudinal movement of the stent; wherein the meansfor rotating the split reed grasper comprises a hand held motor.
 6. Thestent delivery system of claim 5 wherein the split reed grasper isreleasably connected to the stent.
 7. The stent delivery system of claim5 wherein the stent comprises a sheet of nitinol.
 8. The stent deliverysystem of claim 5 wherein stent comprises a sheet of perforatedmaterial.
 9. A stent and stent delivery system for inserting a stentinto a vessel of the body and deploying the stent at a target sitewithin the vessel, said stent delivery system comprising: an insertioncatheter having a lumen; a stent having a small diameter configurationand a large diameter configuration; a split reed grasper attached to ashaft at the distal end of the shaft, said split reed grasper secured tothe stent, wherein rotation of the shaft facilitates moving the stentout of the lumen of the distal end of the insertion catheter; and ameans for rotating the shaft; wherein the means for rotating the shaftcomprises a hand held motor.
 10. The stent delivery system of claim 9wherein the split reed grasper is releasably connected to the stent. 11.The stent delivery system of claim 9 wherein the stent comprises a sheetof nitinol.
 12. The stent delivery system of claim 9 wherein stentcomprises a sheet of perforated material.